An internal combustion engine is provided with an exhaust system, which serves the function of introducing the gases produced by the combustion into the atmosphere, thus limiting both the noise and the content of pollutants. A modern exhaust system comprises at least one muffler, which typically has an elliptical section and is provided with at least one inlet opening and at least one outlet opening. A labyrinth which determines a path for the exhaust gases from the inlet opening to the outlet opening is defined within the muffler; such a labyrinth is normally formed by diaphragms (or baffles), transversally or longitudinally arranged to define chambers, and (possibly laterally perforated) pipes which connect the chambers to one another.
The back pressure generated by the muffler (i.e. the pressure loss determined in the exhaust gases passing through the muffler) exponentially grows as the engine speed (revolutions) increases (i.e. as the average speed of the exhaust gases increases). Accordingly, fuel consumption and direct CO2 emissions are penalized due to the back pressure generated by the muffling body in order to reduce noise emissions. To obviate this drawback, it has been suggested to construct an exhaust system (e.g. described in U.S. Pat. No. 5,301,503A1) with two differentiated paths according to the engine speed, so that at low speeds (low exhaust gas pressure) the exhaust gases follow a first high acoustic attenuation (i.e. high back pressure) path, while at high speeds (high exhaust gas pressure), the exhaust gases follow a second low acoustic attenuation (i.e. low back pressure) path. In an exhaust system with two differentiated paths, a control valve is provided, which is adapted to alternatively direct the exhaust gases along the desired path according to the engine speed. These control valves usually include the use of an electric, electro-pneumatic or similar actuator, which is driven by an electronic control unit of the engine to move the position of one or more baffles which direct the exhaust gases into the exhaust system.
It has been observed that the reliability of the control valves is restricted over time; in fact, because of mechanical and thermal stresses typical of the exhaust systems, and due to scaling formed by the exhaust gases, the known control valves tend to stick or in any case they work in a manner other than that envisaged in the step of designing. Furthermore, due to the presence of an electric or electro-pneumatic actuator, the known control valves are heavy and large in size (also because the electric or electro-pneumatic actuator needs to be thermally and mechanically protected) and their cost is considerably high (also because of the need to provide the wiring/electro-pneumatic connection of the electric/electro-pneumatic actuator in a region of the vehicle which undergoes considerable heating and is exposed to the road surface).